You might have better luck with the fast-logger library, for one. I'd also suggest using ansi-wl-pprint, which would work on Windows and also probably be faster than string concatenation (which is just plain bad in Haskell).

As was pointed out, GHC is calling getCurrentTime too often. If you take advantage of GHC's laziness, the value will stay valid longer. I assume that is what fast-logger does.

https://hackage.haskell.org/package/fast-logger